1. Technical Field
The present disclosure relates to a semiconductor element used under a high current and a high voltage.
2. Description of the Related Art
A group-III nitride semiconductor is a useful material for a heterostructure field effect transistor (HFET) used under a high current and a high voltage, since the group-III nitride semiconductor has a larger bandgap and a breakdown field than a conventional semiconductor, such as a silicon (Si) semiconductor.
In the group-III nitride HFET, the two dimensional electron gas (2DEG) generated at a heterojunction interface between, for example, an aluminum gallium nitride (AlxGa1-xN (0≤x≤1)) electronic barrier layer and a gallium nitride (GaN) channel layer is used as a channel. To provide a normally-off property to the group-III nitride HFET, a recess is created in the electronic barrier layer to reduce a charge caused by piezoelectric polarization at the heterojunction interface, and a p-type layer, such as a p-GaN layer, is formed at the recess (PTL 1).
Meanwhile, an HFET with a higher carrier density is expected to be used under a further higher current. For example, the carrier density can be increased by increasing spontaneous polarization of the electronic barrier layer. Indium aluminum gallium nitride (InxAlyGa1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1)) that can be lattice-matched with GaN and can achieve larger spontaneous polarization than AlGaN by adjusting the composition is expected to be used for an electronic barrier layer of the group-III nitride HFET (PTL 2).
Hereinafter, InxGa1-xN (0<x<1), AlyGa1-yN (0<y<1), and InzAl1-zN (0<z<1), which are all ternary mixed crystals, are respectively abbreviated as AlGaN, AlGaN, and InAlN unless the composition is specified. The InxAlyGa1-x-yN (0<x<1, 0<y<1, 0<x+y<1), which is a quaternary mixed crystal, is abbreviated as InAlGaN.